ADVANCED MATURITY OF ‘PERLETTE’ TABLE GRAPES BY TRAINING SYSTEMS WHICH INCREASE FOLIAGE EXPOSURE TO SUNLIGHT

Abstract

Although extensive work has been reported on winegrapes (Vitis vinifera L.) regarding canopy structure, management and microclimate on berry ripening and composition, scarce information has been devoted to this issue in tablegrapes. Canopy microclimate, photosynthesis and other physiological traits were determined in three year old ‘Perlette’ vines trained on a T-trellis, in Sonora, México. In the undivided commercial T-trellis UTT) vine canopy, the photosynthetic photon flux densities (PPFD) reaching external, middle and internal leaf layers were 1922, 53 and 34 μmol m^-2 s^-1, respectively. In the same order, net photosynthesis (Pn) rates were 19.0, 1.7 and 1.0 μmol CO₂ m^-2 s^-1, while chlorophyll contents were 1.9, 1.7 and 1.0 mg mL^-1. No differences in total protein content were found between leaf layers, but significant differences in rubisco specific activity were found among external, middle and internal leaves, reaching 1.07, 0.65 and 0.25 μmol min^-1 mg^-1, respectively. Four training systems were compared against a commercial undivided T-trellis (UTT): Slanted pergola (Pergola), a specifically designed system (CIAD), Lyre (Lyre) and a divided T-trellis (Divided). Significant differences in PPFD on Lyre, Pergola, CIAD, Divided and UTT yielded 2192, 2076, 1900, 885 and 711 μmol m^-2 s^-1. At véraison, Pn in Pergola, CIAD, Lyre, Divided and UTT was 12.7, 11, 12.5, 10.5 and 5.1 μmol CO₂ m^-2 s^-1, respectively. Five days after harvest, Pn showed a decrease in all training systems, particularly in UTT which showed only 3.7 μmol CO₂ m^-2 s^-1. Stomatal resistance at véraison and postharvest was highest in UTT with 4.2 and 6.8 s cm^-1 for both periods. Total soluble solids by 27 April were 15.7 °Brix for CIAD, while for UTT was only 12.1 °Brix. A week later, CIAD, Lyre, Pergola and Divided reported 16.3, 15.9, 15.5 and 15.2 °Brix, while UTT reached only 13.1 °Brix. Thus by dividing canopies and applying canopy management techniques the harvest date in the early season seedless grapes can be advanced, by increasing light harvest, photosynthetic rate and berry sugar accumulation.